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Friday, 27 July 2012

Ileus

The term ileus appears to have undergone a subtle change in meaning/usage. The term Ileus originally was used to denote stasis of bowel contents. The term had two common uses
  • Adynamic Ileus ( syn paralytic ileus, non-obstructive ileus)
This referred to non-functioning bowel for reasons other than obstruction
  • Obstructive Ileus
This referred to stasis of bowel contents for reasons related to obstruction

Adynamic Ileus ----------> was shortened to ----------> Ileus
Obstructive Ileus----------> was shortened to ----------> obstruction


  • Motility Disorder
This term refers to abnormal motility of bowel contents without specifying whether it is obstructive or non-obstructive in nature.

The hallmark of small bowel obstruction is the presence of gaseous loops of small bowel which are distended over 30mm. The absorptive capacity of the small bowel is so great that even extreme amounts of air swallowing will not distend normal small bowel.



Correlation with patient history and clinical signs can assist in arriving at a more specific diagnosis. The difficulty in differentiating obstruction from ileus has led some radiologists to use the blanket term "motility disorder" when describing dilated loops of bowel.

The bowel could reasonably be said to be a very sensitive organ. It has a propensity to stop functioning with little provocation. Amongst the possible causes are infection (anywhere), abdominal inflammation, chemical/pharmacological causes, post-operation peritonitis, electolyte imbalance, and trauma. 
Abdominal surgery commonly results in generalised adynamic ileus in which the bowel is temporarily non-functioning. This typically manifests on around day 4 post-op.


ADYNAMIC / PARALYTIC ILEUS

The appearance of generalised adynamic ileus on plain film is quite characteristic. The large and small bowel are extensively airfilled but not dilated. This is often described as the large and small bowel "looking the same".

LOCALISED ILEUS / SENTINEL LOOP SIGN
The cause of the inflammation is unknown but would be typical of ulcerative colitis or Crohn's disease. This appearance is known as "thumbprinting".

Just inferior to the diseased segment of colon are a few prominent air-filled loops of jejunum. It is possible that this is localised ileus of the jejunum associated with the diseased colon. This is known as "sentinel sign".


SMALL BOWEL OBSTRUCTION

Vomiting may release some of the proximal bowel contents and reduce the amount of proximal dilation. The bowel hyperperistalses. Bowel distal to the point of obstruction (i.e. colon and sometimes distal small bowel) empties over time. Strangulation of the bowel may result from vascular compromise of the affected loops and is a cause of increased mortality.

Causes: Overwhelmingly, the most common cause of a mechanical small bowel obstruction are adhesions related to prior surgery /appendectomy, colorectal surgery and gynecologic surgery/ (60%). Hernias Most often femoral or inguinal.   Intussusception. Volvulus. Tumor, either primary or metastatic. Wall lesions such as leiomyomas or strictures. Crohn’s disease.Foreign bodies. Gallstones.

  Imaging findings:
o       Conventional radiography is the study of first choice
§         Loops proximal to the point of obstruction will become dilated and fluid-filled
·         Usually greater than 2.5-3 cm in size
§         Differential height of air-fluid levels in the same loop of small bowel no longer considered reliable sign of mechanical SBO
§         Absence of, or disproportionately smaller amount of, gas in the colon, especially the rectosigmoid
§         Loops of small bowel may arrange themselves in a step-ladder configuration from the left upper to the right lower quadrant in a distal SBO
§         Mostly fluid-filled loops of bowel may demonstrate a string-of-beads sign caused by the small  amount of visible air in those loops





Closed-loop obstructions
o       Most (75%) are caused by adhesions
o       In a closed-loop obstruction, the twisted loop itself remains dilated with gas and fluid thus producing a dilated, U-shaped loop of small bowel
§         Does not change in position or size over time
·         Coffee bean sign or pseudotumor may be seen
o       Closed-loop obstructions are not usually diagnosable by conventional radiography and require CT
§         CT findings may include a U- or C-shaped loop of small bowel
§         A spoke-like configuration of the mesentery demonstrating stretched vessels converging on the site of the twist may be seen
·         The appearance of the tightly twisted mesentery has been called the whirl sign
§         The beak sign may be seen as a fusiform tapering at the site of the obstruction
·         Treatment of small bowel obstruction
o       Many patients are treated conservatively with small bowel decompression and intravenous fluids
o       Surgical intervention may be necessary if there are signs and symptoms of strangulation, peritonitis or lack of response to conservative treatment




Differentiating SBO from Paralytic Ileus

SBO
Ileus
Etiology
Patient with prior surgery weeks to years prior
Recent (hours) post-operative patient
Pain
Colicky
Not a prominent feature
Abdominal distension
Frequently prominent
Sometimes not apparent
Bowel sounds
Usually increased
Usually absent
Small bowel dilatation
Present
Present
Large bowel dilatation
Absent
Present


Large bowel obstruction

The most common causes of large bowel obstruction are colo-rectal carcinoma and diverticular strictures.  Less common causes are hernias or volvulus (twisting of the bowel on its mesentery). Adhesions do not commonly cause large bowel obstruction.
Radiological appearances of large bowel obstruction differ from those of small bowel obstruction, however, with large bowel obstruction there is often co-existing small bowel dilatation proximally.
Dilatation of the caecum >9cm, and >6cm for the rest of the colon is considered abnormal.

Volvulus

Twisting of the bowel, or volvulus, is a specific cause of bowel obstruction which can have characteristic appearances on an abdominal X-ray.
The two commonest types of bowel twisting are sigmoid volvulus and caecal volvulus.

Sigmoid volvulus

Unlike the majority of the large bowel, the sigmoid colon has its own mesentery. It is therefore more prone to twisting at the root of its mesentery, which is located in the left iliac fossa. The result is the formation of an enclosed bowel loop which becomes dilated. If untreated this can lead either to perforation due to excessive dilatation, or to ischaemia due to compromise of the blood supply.
Sigmoid volvulus - coffee bean sign 

Caecal volvulus

The caecum is most frequently a retroperitoneal structure, and therefore not susceptible to twisting. However, in up to 20% of individuals there is congenital incomplete peritoneal covering of the caecum with formation of a 'mobile' caecum on a mesentery, such that it no longer lies in the right iliac fossa. This is a normal variant but is associated with increased incidence of folding or twisting of the caecum (caecal volvulus), which may be complicated by obstruction, vascular compromise, or perforation. 

Bowel wall inflammation

Occasionally, abdominal X-rays show signs of inflammation in patients with inflammatory bowel disease. Abnormalities may relate to either acute or chronic stages of disease.
  • Abdominal X-rays sometimes demonstrate signs of bowel inflammation such as mucosal thickening 'thumb-printing' or a featureless colon 'lead pipe' colon.
Mucosal thickening - 'thumbprinting' - ACUTE EXACERBATION
Lead pipe colon - CHRONIC INFLAMMATION (ulcerative colitis)
 

Toxic megacolon

Toxic megacolon is a potentially life-threatening condition characterized by dilatation of the large bowel without obstruction, in the context of acute bowel inflammation. This may be due to inflammatory bowel disease, especially ulcerative colitis, or other causes of colitis such as infection.
  Gasless abdomen
Although a gasless abdomen is highly suggestive of a high obstruction, this can also be seen with excessive vomiting, and/or diarrhea.  This picture can also occur in the early stages of appendicitis, as well as in Addisonian crisis (adrenal crisis). Occasionally, this occurs in patients with marked cerebral depression such that their swallowing is impaired.


DISCUSSION
In a mechanical obstruction, there is preferentially more air proximal to the obstruction than distal to it. Thus, in an obstruction, there is either too much gas in the small bowel (and not much gas in the large bowel), or too much gas in the large bowel (and not much gas in the small bowel). In an adynamic ileus, there usually is no preferential collection of air.  There is too much air or not much air in both the small and large bowel.  This pattern of distribution is not necessarily definitive.  When there is too much air in the small bowel, this may be a small bowel obstruction which has been present long enough to have allowed the colon gas to clear. When there is too much air in the colon, this may be a large bowel obstruction (e.g.., sigmoid volvulus) with a competent ileocecal valve.  If, however, there is too  much air in both parts of the bowel, you may have a paralytic ileus, or a large bowel obstruction with an  incompetent ileocecal valve, or a small bowel obstruction which is early or intermittent.

Another important point is that sometimes in a mechanical obstruction, there is very little air present and the intestinal loops are filled with fluid. In these cases, the loops may appear as opaque sausage-like
structures in the abdomen or the bowel may be isodense with the rest of the abdomen showing apaucity of gas.  On the upright view, the air may get trapped in the valvulae conniventes (small bowel plicae circulares [circular folds]) giving a "string of pearls" gas pattern appearance.

SUMMARY

In summary, one should evaluate abdominal films in a stepwise fashion.
 
1.  Look at the fixed anatomy.  Do not forget the lungs.
 
2.  Gas Distribution.
     Obstruction:  Too much air in the small bowel (and not much gas in the large bowel) or too much air in the large bowel (and not much gas in the small bowel).  
Poor gas distribution or gasless.
     Ileus:  Good gas distribution over most of the abdomen.  Too much air in both large and small bowel.  
Warning:  This could also appear in large bowel obstruction with an incompetent ileocecal valve, or in an early or intermittent small bowel obstruction.
 
3.  Bowel Dilatation.
     Obstruction:  Smooth bowel walls (resembles sausages or a hose).  Preferential dilatation of the bowel proximal to the obstruction.
     Ileus:  Dilatation of the bowel in proportion to each other, so that the colon remains larger than the small intestine.  Look for sentinel loops.
 
4.  Air-fluid Levels.
     Obstruction:  Many dilated air-fluid levels in both limbs of a given loop, at different heights (candy canes).
     Ileus:  Fewer and/or smaller (less dilated) air-fluid levels scattered throughout the abdomen.
 
5. Arrangement of loops (supine view only).
     Obstruction:  Dilated loops arranged in "stepladder" fashion.  Orderly.  A bag of sausages.
     Ileus:  Disorderly loops scattered throughout the abdomen.  A bag of popcorn.




SOURCES:
http://www.wikiradiography.com/page/The+Abdominal+Plain+Film-+Ileus
http://www.learningradiology.com/archives06/COW%20216-SBO/sbocorrect.htm
http://radiologymasterclass.co.uk/tutorials/abdo/abdomen_x-ray_abnormalities/pathology_large_bowel_obstruction.html 
http://www.hawaii.edu/medicine/pediatrics/pemxray/v3c18.html





Barium follow-through

Some investigators record the orocecal transit time in an upper gastrointestial and small-bowel follow- through examination, timing the smallbowel transit time from the second cup of barium, whereas others begin the timing from when sufficient barium fills the proximal two loops of jejunum. Although barium normally enters the duodenum within 15 min of ingestion, in patients with dysmotility of the esophagus or stomach, measurement of orocecal transit time will interfere with a true measurement of small-bowel transit time. For the purist, it seems, small-bowel transit time should be measured from the moment barium enters the duodenum.
As with blood pressure measurements, “normal” comprises a range of values. Ideally, one would compare the small-bowel study in question with the patient’s previous study during a period of good health to determine whether the small-bowel transit time is normal.
Small-bowel transit time depends on many factors including density and temperature of the barium preparation and presence of chemical additives, stress, patient age, patient positioning during the study, and the use of pharmacologic agents. However, the most important factors, which inversely correlate with small-bowel transit time, are the volume of barium ingested and maintenance of a full stomach.
The diseases accounting for rapid smallbowel transit time (e.g., giardiasis, carcinoid syndrome,
graft-versus-host disease) or prolonged small-bowel transit time (e.g., hypothyroidism, scleroderma, intestinal pseudoobstruction). 


_In the largest radiologic study of small-bowel transit time that comprised 315 normal small-bowel
examinations, a mean small-bowel transit time of 84 min (range, 15 min to 5 hr) was found. In 83% (261/315) of these examinations, the small-bowel transit time was less than or equal to 2 hr, whereas 97% (304/315) reached the terminal ileum within 3 hr. Small-bowel transit time was less than 30 min in only 5% (17/315). In two other radiologic studies, comprising 87 patients, small-bowel transit time ranged from 33 to 167 min, and from 15 to 105 min.

Most patients have a small-bowel transit time of between 30 min and 3 hr. The minority of cases, in which the small-bowel transit time lies outside of this range, should not absolutely be diagnosed as abnormal without correlation with associated radiographic and clinical findings.


SOURCE:
http://www.ajronline.org/content/174/3/866.1.full.pdf

LINKS:
http://www.wikiradiography.com/page/The+Abdominal+Plain+Film-+Ileus
http://www.learningradiology.com/archives06/COW%20216-SBO/sbocorrect.htm
http://radiology.rsna.org/content/26/3/342.extract
http://radiologymasterclass.co.uk/tutorials/abdo/abdomen_x-ray_abnormalities/pathology_small_bowel_obstruction.html

Sunday, 22 July 2012

Breast Imaging

Brief notes (Radiologia-Frater Lorand)

Examination techniques:

Native film / digital mammography - 
  • High linear contrast resolution, makes differentiation bw structures of almost identical X-ray attenuation properties possible (fat, glands, connective tissue).
  • Small focus, fine granulation film are used.
  • Best time to perform it is in the second week of the menstrual cycle.
  • By compressing the breast the radiation burden also slightly decreases.
  • 45-65 year old females biannually.
  • High risk pt. if started menstruation before 12 years of age, or if entered menopause after 65 years of age. Pregnancy after 65 years of age. 
Contrast enhanced examinations:
  • Ductography: injection of iodinated (felszivodo) contrastagent
  • Pneumocystography: injection of air - for intra-cystic tumors
Ultrasound: 
  • Allows for guided biopsy.
  • Helps in examining dense, fibrotic, glandular breasts.
  • Can be the initial examinations in patients <30.
  • Disadvantages: scar and tumor can give similar appearance, microcalcifications are not always visible.
MRI:
  • Less linear contrast resolution compared to traditional mammography.
  • Used to differentiate between scar and tumor, to assess implants.
CT:
  • Deeply situated lesions, close to the pectoral muscle.
Nuclear medicine:
  • To detect small, non palpable lesions.
  • To detect lymphatic spread.
Invasive diagnostics:
  • Fine needle biopsy: cytology and cellular analysis.
  • Core biopsy: if the result of the above is not decisive.
  • Cyst puncture: air injected, stops refilling.
Benign tumors:
  •  Fibroadenoma:
Most common, looks like a cyst on a mammogram, oval, sometimes lobulated, sometimes has large calcifications, if > 2 cm then remove it.
  • Lipoma:
  • Intraductal papilloma: 
Can turn malignant. Located in the ducts.

Malignant tumors:
  • Intraductal carcinoma - most common
  • Lobular, medullary, mucinous, and papillary tumors are less common
  • Features: spiculated, blurred contour, microcalcifications, intraductal calcifications, decreased echogenicity on US.
  • Sarcomas: are extremly rare.
  • Source of metastases to the breasts: LUNGS, MELANOMA, LYMPHOMA (mostly non-Hodgkin). 

Wednesday, 4 April 2012

Urine jet


Doppler image of a urine jet arriving from the right ureteral orifice

Monday, 20 February 2012

Intima-Media thickness

An intima-media thickness of < 1 mm is normal.   

IMT predicts cardiovascular risk
Used by pharmaceutical research groups for evaluating the regression and/or progression of atherosclerotic cardiovascular disease.
IMT is strogly associated to atherosclerosis.
It is worth noting that not all the processes of thickening of the intima-media are due to atherosclerosis. Intimal thickening is in fact a complex process, depending on a variety of factors, not necessarily related to atherosclerosis. Local hemodynamics plays an important role, higher blood pressure and changes in shear stress being potential causes of intimal thickening, even differences in cholesterol homeostasis.
Often, the measurement of the IMT is measured in three tracts: in the common carotid, at one or two cms from the flow divider, at the bifurcation and in the internal carotid artery.
IMT measurements of the deep wall, by ultrasound, are generally more reliable than measurements performed on the outer wall.